Dry chemical fire extinguishers are usually employed to extinguish fires by depressing a lever or a valve stem head on the exterior of the fire extinguisher. This action, in turn, opens a valve in the interior of the fire extinguisher to release pressurized dry chemical material. Fire extinguishers are also equipped with an indicator which can be used to determine if there is sufficient gas pressure within the container to expel the contents. Some types of indicators form a part of and allow limited movement of the valve to visually show whether or not the container is sufficiently charged without opening the valve. An example of such a fire extinguisher is disclosed in U.S. Pat. No. 3,229,851 to Horwitt et al. ("Horwitt").
Notwithstanding the foregoing valve and pressure indicator arrangements, there are still major problems involved with such prior an valves. The dry chemical agents, such as sodium bicarbonate, often leave a residual powder in the vicinity of the valve seat. Consequently, the valve may no longer properly seal of the valve seat leading to a slow, but steady, loss of pressure from within the container. Additionally, the valve stem may no longer be free to move axially, reducing the accuracy of the indicator. In the valve disclosed by Horwitt, dry chemical powder is free to communicate with an O-ring seal 26. The powder thus forms a residue about the O-ring 26 and the sealing section 21 of sleeve 19. Eventually this residue will foul up the axial movement of the valve stem.
This residue build up could lead to a false negative test from the pressure indicator if the valve stem 24 were stuck in the depressed position shown in FIG. 4. Worse yet, a false positive test may result if the residue prevents the valve stem from being depressed from the position shown in FIG. 2, leading the user to conclude that a sufficient amount of pressure is contained within the fire extinguisher when, in fact, there may be no such pressure.
It is, therefore, an object of the present invention to provide an indicator valve that permits repeated testing of the pressurized container to ensure that it has sufficient pressure, while simultaneously preventing the dry chemical powder from fouling the axial movement of the valve stem.
It is an object of the present invention to provide a so-called pindicator-type valve that requires less pans and, thus, is smaller and easier to manufacture. It is still a further object of the present invention that the pindicator-type valve arrangement be simple and cost effective to manufacture, yet reliable and efficient in use.